Mine is only rated at 16/25 (2009 V70 3.2). I have only had it for about 2 weeks, but I am averaging just under 24mpg in mixed driving (average speed 24mph according to the trip computer). The average shoots up when I drive highay at the speed limit (65mph here) and I think it will do very nearly 30mpg with a very disciplined foot. With less discipline (call it 72mph which is closer to average flow) the 25mpg is probably quite realistic. I have always done better than EPA in my cars so I think the 3.2 will be tolerable...as long as I don't let my wife drive it. Drive 75 to 80mph in the left lane and fuel economy clearly isn't your first priority in any vehicle, so take what you get. Slow down and you will likely meet your desired range. It's not like you have to rush to escape an uncomfortable seat or something. ;)

I would have preferred the 2.5 turbo instead of the 3.2 N/A. It would have been off boost most of the time in my hands so lower displacement would have been to my benefit. But as much as I loathe automatic transmissions in general, I like how the 6-speed A/T has adapted to my own sedate driving style. It shifts right up to the tall gears and holds them better than I would have expected. That does a bit to offset the extra displacement. Plus the whole package does a nice job when I just want to get out of the way (or make my wife slightly uncomfortable, which is a good yard stick.)

In short, I think that the engine is going to be what you make of it. At high speed (which requires enough power to load it up) there is no mechanical reason that the 3.2 would burn fuel significantly less efficiently than something smaller. At 80mph you are fighting aerodynamic drag more than thermodynamic efficiency. The benefits of a smaller powerplant would be more evident around town and at more sedate higway speeds where the big I6 is just loafing along and fighting its own throttle plate. But that doesn't change the fact that you will see better fuel economy at lower speeds either way. This is why, as always, YMMV.

Tim